Electric automobile

ABSTRACT

An electric vehicle includes a motor unit to drive a wheel. The electric vehicle also includes a control system that controls the motor unit. The control system includes an inverter. The electric vehicle also includes a temperature sensor to sense temperature Tmc of the motor coils of the motor unit or a temperature sensor to sense temperature Tic of the inverter. The electric vehicle also includes a limiter to, if the temperature Tmc sensed by the sensor exceeds a motor coils temperature threshold, reduce a motor current of the unit until a derivative dTmc/dt of the sensed temperature Tmc with time t drops to zero or below, or to, if the temperature Tic sensed by the sensor exceeds an inverter temperature threshold, limit a current command to the inverter until a derivative dTic/dt of the sensed temperature Tic with time t drops to zero or below.

CROSS REFERENCE TO THE RELATED APPLICATIONS

This application is based on and claims the Convention priority toJapanese patent applications No. 2011-039854 and No. 2011-039855, bothfiled Feb. 25, 2011, the entire disclosures of which are hereinincorporated by reference as a part of this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric vehicle, such as anin-wheel motor vehicle, that is equipped with motor(s) to drive wheelsand that may be battery-powered or fuel cell-powered.

2. Description of Related Art

An electric vehicle may experience degradation in performance ormalfunctions of a motor serving as a drive for the vehicle. This cansignificantly affect the travel performance or travel safety. Abattery-powered electric vehicle may include a drive system. The drivesystem may employ an IPM (e.g., Interior Permanent Magnet synchronousmotor). Such an IPM may include a neodymium magnet to provide a highlyefficient performance, thus increasing the maximum travel range that ispossible with a limited battery capacity.

An electric vehicle can typically include a synchronous motor or aninduction motor that may be driven with an AC current converted by aninverter from a DC current supplied from a battery. The inverter, whichcan, in principle, include a plurality of semiconductor switchingdevices, may conduct a large current to drive the motor, thus generatinga significant heat. The characteristics of semiconductor switchingdevices may considerably vary with temperature. Overheat may even damagethe semiconductor switching devices. In order to address these, aninverter is typically equipped with a cooling system.

In the past, an in-wheel motor drive system has been proposed in which,to ensure reliability, the temperature of components such as a wheelbearing, a reducer and a motor may be measured and monitored foroverload, with features to limit a drive current in/to the motor or arotational frequency of the motor according to the temperaturemeasurements (see the Patent Document 1 listed below).

[Patent Document 1] JP Laid-open Patent Publication No. 2008-168790

SUMMARY OF THE INVENTION

The driving conditions of an electric vehicle may constantly change,resulting in significant fluctuations of the rotational frequency of amotor and/or the current flow in motor coils. An electric vehicle may bean in-wheel electric vehicle. A motor mounted to an in-wheel electricvehicle may have to operate in a severe environment. For example, such amotor may be constantly subject to externally-induced vibrations becauseit is positioned below suspension springs or it is unsprung. An electricvehicle may be driven for a continuous time with a higher torquegenerated by a motor operating in such a severe environment, in orderto, for example, go up a slope. This leads to increase in thetemperature of a motor, possibly deteriorating the insulation on themotor coils. Thus, managing the temperature of a motor can be a key toachieving the travel safety of a vehicle.

As noted above, an inverter for an electric vehicle is typicallyequipped with a cooling system. Such a cooling system can preventexcessive increase of temperature during a normal operation. However, anelectric vehicle is often driven for a continuous time with a highertorque in order to, for example, go up a slope. In such a case, aninverter may cause overheat by conducting a large current. This mayundesirably change the characteristics of the inverter and/or evendamage the inverter. This, in turn, may lead to undesirable change inthe control characteristics of the driving of a motor and/or lead to asituation where the driving of a motor is impossible.

As discussed earlier, an in-wheel motor drive system may be configuredsuch that the temperature of a motor or an inverter is measured andmonitored for overload, in order to impose a corresponding limit on acurrent used to drive the motor. Such a configuration, however, maydrastically hinder the driving of a vehicle.

An object of the present invention is to provide an electric vehiclewhich can manage the temperature of a motor unit without drasticallyhindering the driving of the vehicle, prevent the change ofcharacteristics of an inverter and/or a damage to the inverter that maybe caused by overheat, thus preventing undesirable change in the controlcharacteristics of the driving of the motor unit and/or preventing asituation where the driving of the motor unit is impossible, and/orenable appropriate measures to be promptly taken. The general aspects ofthe present invention will now be described using the reference signs inthe figures showing embodiments of the present invention.

The present invention may provide an electric vehicle which includes amotor unit 6 configured to drive a wheel 2. The motor unit 6 includesmotor coils 78. The electric vehicle also includes a control system U1that controls the motor unit 6. The control system U1 includes aninverter 31. The electric vehicle also includes a temperature sensor Smathat is associated with the motor coils 78 of the motor unit 6 and isconfigured to sense temperature Tmc of the motor coils 78 or atemperature sensor Sia that is associated with the inverter 31 and isconfigured to sense temperature Tic of the inverter 31. The electricvehicle also includes a limiter configured to, if the temperature Tmcsensed by the temperature sensor Sma exceeds a motor coils temperaturethreshold, reduce a motor current of the motor unit 6 until a derivativedTmc/dt of the sensed temperature Tmc with time t drops to zero orbelow, or to, if the temperature Tic sensed by the temperature sensorSia exceeds an inverter temperature threshold, limit a current commandto the inverter 31 until a derivative dTic/dt of the sensed temperatureTic with time t drops to zero or below. The limiter used in this contextrefers to a motor current reducer 95 or an inverter limiter 102.

In the aforementioned configuration, the temperature sensor Sma maycontinuously sense the temperature Tmc of the motor coils 78 of themotor unit 6, and the temperature sensor Sia may continuously sense thetemperature Tic of the inverter 31. The electric vehicle may be drivenfor a continuous time with a higher torque in order to, for example, goup a slope. This can lead to increase in the temperature Tmc (Tic) ofthe motor coils 78 and the inverter 31. The limiter may determine if thesensed temperature Tmc (Tic) exceeds a predefined threshold.

In a configuration where the limiter is a motor current reducer 95, themotor current reducer 95 may, upon determining that the sensedtemperature Tmc exceeds the motor coils temperature threshold, carry outcontrol that reduces the motor current of the motor unit 6.Subsequently, the motor current reducer 95 may, upon detecting the signthat the rate of change of the sensed temperature Tmc is dropping tozero or below or if the rate of increase of the temperature representedby the aforementioned dTmc/dt drops to zero or below, stop carrying outthe control that reduces the motor current, without waiting for thesensed temperature Tmc itself to drop down to a certain value. Thisprevents drastic hindrance of the driving of the motor unit 6.

If the sensed temperature Tmc of the motor coils 78 begins to increaseonce the motor current reducer 95 stops carrying out the aforementionedcontrol, the motor current reducer 95 may, once the sensed temperatureTmc equals or exceeds the motor coils temperature threshold, resumecarrying out the control that reduces the motor current of the motorunit 6. Subsequently, the motor current reducer 95 may, if theaforementioned rate of increase of the temperature drops to zero orbelow, stop carrying out the control that reduces the motor current.This ensures that overload is avoided.

In a configuration where the limiter is an inverter limiter 102, theinverter limiter 102 may determine if the sensed temperature Tic exceedsa predefined inverter temperature threshold. The inverter limiter 102may, upon determining that the sensed temperature Tic exceeds theinverter temperature threshold, carry out control that limits a currentcommand to the inverter 31. In a particular embodiment, the control maycause change in at least one of duty cycle and pulse number. Forexample, the control that limits a current command to the inverter 31may include reduction of a duty cycle, which indicates pulse ON time perswitching period, below a predefined duty cycle, thus reducing effectivevoltage value, or may include generation of pulses of unequal widthwhile maintaining a switching period.

Subsequently, the inverter limiter 102 may, upon detecting the sign thatthe rate of change of the sensed temperature Tic is dropping to zero orbelow or if the rate of increase of the temperature represented by theaforementioned dTic/dt drops to zero or below, stop carrying out thecontrol that limits a current command to the inverter 31, withoutwaiting for the sensed temperature Tic itself to drop down to a certainvalue. This can avoid excessive reduction of a motor current, thuspreventing drastic hindrance of the driving of the motor unit 6. If thesensed temperature Tic of the inverter 31 begins to increase after theinverter limiter 102 stops carrying out the aforementioned control, theinverter limiter 102 may, once the sensed temperature Tic equals orexceeds the inverter temperature threshold, resume carrying out thecontrol that limits a current command to the inverter 31. Subsequently,the inverter limiter 102 may, if the aforementioned rate of increase ofthe temperature drops to zero or below, stop carrying out the controlthat limits a current command to the inverter 31. This ensures thatoverload is avoided. In this way, the change of characteristics of theinverter 31 and/or a damage to the inverter 31 that may be caused byoverheat can be prevented, thus preventing undesirable change in thecontrol characteristics of the driving of the motor unit and/orpreventing a situation where the driving of the motor unit isimpossible.

The control system U1 may include an ECU which is an electronic controlunit configured to perform general control of the vehicle and may alsoinclude an inverter unit 22, with the inverter unit 22 including a powercircuitry 28 which includes the inverter 31 and also including a motorcontrol circuitry 29 configured to control at least the power circuitry28 in accordance with control from the ECU 21, wherein the inverter maybe configured to convert a DC power from a battery unit into an AC powerused to drive the motor unit.

The motor control circuitry 29 may include the limiter 95 (102), whereinthe limiter may include a determiner 39 (39A) configured to determine ifthe temperature Tmc (Tic) sensed by the temperature sensor Sma (Sia)exceeds the motor coils temperature threshold or the invertertemperature threshold and may also include a controller 40 (40A)configured to send to the power circuitry 28, if it is determined thatthe sensed temperature Tmc (Tic) exceeds the motor coils temperaturethreshold or the inverter temperature threshold, a command that reducesthe motor current of the motor unit 6 or a command that limits thecurrent command to the inverter 31.

With a configuration where the motor control circuitry 29 of theinverter unit 22 includes the limiter which may be the motor currentreducer 95 or the inverter limiter 102, the motor current reducer 95 orthe inverter limiter 102 that may make the aforementioned determinationbased on the sensed temperature is positioned closer to the motor unit 6than with a configuration where the ECU 21 includes the limiter, thusthe former configuration being more advantageous in terms of wirerouting. Also, with a configuration where the motor control circuitry 29of the inverter unit 22 includes the limiter, an appropriate control canbe initiated more quickly than with a configuration of the ECU 21including the limiter, thus promptly avoiding various driving problems.Furthermore, with the former configuration, the load on the ECU 21,whose complexity is increasing hand-in-hand with its sophistication, canbe reduced.

The inverter unit 22 may include an abnormalities notifier 41 configuredto send to the ECU 21 a notification of abnormalities of the motor unit6 if the determiner 39 determines that the sensed temperature exceedsthe motor coils temperature threshold or a notification of abnormalitiesof the inverter 31 if the determiner 39A determines that the sensedtemperature exceeds the inverter temperature threshold. The ECU 21performs general, integrated control of the vehicle. Thus, by sending tothe ECU 21 a notification of abnormalities of the motor unit 6 if it isfound, with the motor current reducer 95 that may be included in theinverter unit 22, that there is abnormalities of the motor coils 78 orby sending to the ECU 21 a notification of abnormalities of the inverter31 if it is found, with the inverter limiter 102 that may be included inthe inverter unit 22, that there is abnormalities of the inverter 31,the ECU 21 can correspondingly perform an appropriate control of thevehicle in general. Also, the ECU 21 is an upper-level control unitwhich may send a drive command to the inverter unit 22. Thus, an urgentcontrol performed by the inverter unit 22 may be followed by a moreappropriate control of drive which is performed by the ECU 21. In someembodiments, the ECU 21 may include the motor current reducer 95 or theinverter limiter 102.

A wheel bearing unit 4 and a reducer unit 7 may further be provided,wherein the motor unit 6, together with the wheel bearing unit 4 and thereducer unit 7, may form an in-wheel motor drive system 8 that is partlyor entirely disposed within the wheel 2. Reliability of the wheelbearing unit 4, the reducer unit 7 and the motor unit 6 is an urgentconcern for an in-wheel motor drive system 8 which, due to its smallersize, has less materials used, involves rapid rotation of the motor unit6, and etc. Sensing the temperature of the motor coils 78 andcontinuously monitoring the motor coils 78 for abnormalities such asdeterioration of insulation enables responsive control thatappropriately reduces the motor current of the motor unit 6. In additionor alternatively, sensing the temperature of the inverter 31 andcontinuously monitoring the inverter 31 for abnormalities that may becaused by overheat, such as thermal runaway caused by overheat ofsemiconductor switching devices enables responsive control thatappropriately limits a current command to the inverter 31.

A reducer unit 7 may be provided which is configured to produce rotationwith a speed that is reduced with respect to that of rotation of themotor unit 6, wherein the reducer unit 7 may comprise a cycloidalreducer. Such a configuration in which the reducer unit 7 comprises acycloidal reducer having, for example, a reduction ration of 1/6 orgreater, allows for the provision of a smaller motor unit 6, thusachieving reduction in dimensions of the system or assembly. With such asignificant reduction ratio, a smaller motor unit 6 may involve rapidrotation. Even when a motor unit 6 is undergoing rapid rotation, thechange of characteristics of an inverter 31 and/or a damage to theinverter 31 can be prevented, thus preventing undesirable change in thecontrol characteristics of the driving of the motor unit and/orpreventing a situation where the driving of the motor unit isimpossible. This enables avoiding a situation where driving of a vehicleis suddenly impossible.

The present invention encompasses any combination of at least twofeatures disclosed in the claims, the specification and/or the drawings.In particular, the present invention encompasses any combination of atleast two claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In any event, the present invention will become more clearly understoodfrom the following description of embodiments thereof, when taken inconjunction with the accompanying drawings. However, the embodiments andthe drawings are given only for the purpose of illustration andexplanation, and are not to be taken as limiting the scope of thepresent invention in any way whatsoever, as defined by the appendedclaims. In the accompanying drawings, like reference numerals are usedto denote like parts throughout the several views, and:

FIG. 1 is a block diagram of a schematic configuration of an electricvehicle, as viewed from top, according to the first embodiment of thepresent invention;

FIG. 2 is a block diagram of a schematic configuration of severalfeatures including an inverter unit for the electric vehicle shown inFIG. 1;

FIG. 3 is a block diagram of a controllers segment for the electricvehicle shown in FIG. 1;

FIG. 4A is a characteristic diagram showing a relationship between timeand the temperature of motor coils of a motor unit for the electricvehicle shown in FIG. 1;

FIG. 4B is another characteristic diagram showing a relationship betweentime and the temperature of motor coils of a motor unit for the electricvehicle shown in FIG. 1;

FIG. 5 is a front cut-away view of an in-wheel motor drive system forthe electric vehicle shown in FIG. 1;

FIG. 6 is a longitudinal cross sectional view of FIG. 5 taken along theline VI-VI, illustrating a motor;

FIG. 7 is a longitudinal cross sectional view of FIG. 5 taken along theline VII-VII, illustrating a reducer;

FIG. 8 is a fragmentary enlarged cross sectional view of FIG. 7;

FIG. 9 is a block diagram of a schematic configuration of severalfeatures including an ECU, of an electric vehicle according to thesecond embodiment of the present invention;

FIG. 10 is a block diagram of a schematic configuration of severalfeatures including an inverter unit, of an electric vehicle according tothe third embodiment of the present invention;

FIG. 11 is a block diagram of a controllers segment for the electricvehicle shown in FIG. 10;

FIG. 12A is a characteristic diagram showing a relationship between timeand the temperature of an inverter unit for the electric vehicle shownin FIG. 10;

FIG. 12B is another characteristic diagram showing a relationshipbetween time and the temperature of an inverter unit for the electricvehicle shown in FIG. 10; and

FIG. 13 is a block diagram of a schematic configuration of severalfeatures including an ECU, of an electric vehicle according to thefourth embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

An electric vehicle according to the first embodiment of the presentinvention will now be described in connection with FIG. 1 to FIG. 8. Theillustrated electric vehicle is a four-wheel vehicle that includes avehicle body 1 with left and right rear wheels 2 and left and rightfront wheels 3, with the rear wheels 2 being drive wheels and the frontwheels 3 being steered driven wheels. The drive wheels 2 and the drivenwheels 3, both equipped with tires, are supported by the vehicle body 1via respective wheel bearing units 4, 5. In FIG. 1, the wheel bearingunits 4, 5 are labeled with “H/B” which is an abbreviation for hubbearing. The left and right drive wheels 2, 2 are driven by respectiveindependent traction motor units 6, 6. Rotation of a motor unit 6 istransmitted via a reducer unit 7 and a wheel bearing unit 4 to a wheel2. The motor unit 6, the reducer unit 7 and the wheel bearing unit 4 areintegrally assembled with each other to form an in-wheel motor drivesystem 8 that is partly or entirely disposed within the wheel 2. Thein-wheel motor drive system 8 may be referred to as an in-wheel motorunit. The motor unit 6 may, without the interposition of the reducerunit 7, directly drive the wheel 2 into rotation. The wheels 2, 3 areequipped with respective electromechanical brakes 9, 10.

The left and right front steered wheels 3, 3 are turnable via a turningmechanism 11 and are steered with a steering mechanism 12. The turningmechanism 11 includes left and right knuckle arms 11 b, 11 b holding therespective wheel bearing units 5 and also includes a tie rod structure11 a configured to be laterally displaced to change the angles of theleft and right knuckle arms 11 b, 11 b. The lateral movement of theturning mechanism 11 may be caused by a command from the steeringmechanism 12, which drives an EPS (Electric Power Steering) motor 13,and via a rotary to linear motion converter mechanism (not shown). Asteering angle sensor 15 is configured to sense a steering angle. Theoutput of the steering angle sensor 15 is sent to the ECU 21 in whichthe sensed information may be used to generate anaccelerating/decelerating command for left and right wheels.

As shown in FIG. 5, the in-wheel motor drive system 8 includes a wheelbearing unit 4, a motor unit 6 and a reducer unit 7 interposed betweenthe wheel bearing unit 4 and the motor unit 6, in which the hub of adrive wheel 2 (FIG. 2) supported by the wheel bearing unit 4 iscoaxially coupled with a rotational output shaft 74 of the motor unit 6(FIG. 5). Preferably, the reducer unit 7 has a reduction ratio of 1/6 orgreater. The illustrated reducer unit 7 includes a cycloidal reducerwhich includes a rotational input shaft 82 coaxially connected to therotational output shaft 74 of the motor unit 6. The rotational inputshaft 82 has eccentric segments 82 a, 82 b. The cycloidal reducer alsoincludes curvilinear plates 84 a, 84 b mounted via respective bearings85 to the eccentric segments 82 a, 82 b, in such a way to transmit theeccentric motions of the curvilinear plates 84 a, 84 b in the form of arotary motion to the wheel bearing unit 4. It is to be noted thathereinafter in this specification, terms “outboard” and “inboard”represent one side of the vehicle body away from the longitudinal centerof the vehicle body and the other side of the vehicle body close to thelongitudinal center of the vehicle body, respectively, when assembled inthe vehicle body.

The wheel bearing unit 4 includes an outer member 51 having an innerperiphery formed with a plurality of rows of raceway surfaces 53, aninner member 52 having an outer periphery formed with raceway surfaces54 held in face to face relation to those raceway surfaces 53, and aplurality of rows of rolling elements 55 that are interposed between theraceway surfaces 53 of the outer member 51 and the raceway surfaces 54of the inner member 52. The inner member 52 concurrently serves as a hubfor mounting a drive wheel. The illustrated wheel bearing unit 4includes a double row angular contact ball bearing, in which the rollingelements 55 are in the form of balls rollingly retained by a retainer 56that is provided one for each row of the balls. The raceway surfaces 53and 54 have arcuate cross sectional shapes and are formed to haverespective contact angles held in back-to-back relation with each other.The outer member 51 and the inner member 52 define an annular bearingspace therebetween, and an outboard end of the annular bearing space issealed by a sealing member 57.

The outer member 51, which serves as a stationary member, is of onepiece construction having a flange 51 a for attaching to an outboardhousing 83 b of the reducer unit 7. The flange 51 a has bolt insertionholes 64 formed at a plurality of circumferential locations thereof. Thehousing 83 b has bolt receiving holes 94 that are internally threaded atlocations thereof corresponding to the respective bolt insertion holes64. The outer member 51 can be mounted to the housing 83 b by screwinginto the bolt receiving holes 94 the mounting bolts 65 that arepre-inserted in the bolt insertion holes 64.

The inner member 52, which serves as a rotational member, includes anoutboard member 59 having a hub flange 59 a for attaching a wheel. Theinner member 52 also includes an inboard member 60 which has an outboardside fitted to an inner periphery of the outboard member 59 and which iscrimped to be integrated with the outboard member 59. The outboardmember 59 and the inboard member 60 have the corresponding rows of theraceway surfaces 54 formed thereon. The inboard member 60 has a centerthereof formed with a through bore 61. The hub flange 59 a hasforce-fitting holes 67 at a plurality of circumferential locationsthereof for receiving corresponding hub bolts 66. The outboard member 59has a cylindrical pilot portion 63 for guiding a drive wheel and brakecomponents (both not shown), which is located in the vicinity of theroot of the hub flange 59 a of the outboard member 59 and is protrudingtowards the outboard side. A cap 68 closing an outboard end of thethrough bore 61 is fitted to an inner periphery of the pilot portion 63.

The illustrated motor unit 6 includes a radial-gap type, IPM motor(e.g., an Interior Permanent Magnet synchronous motor) that includes amotor stator 73 fitted to a cylindrical motor housing 72 and alsoincludes a motor rotor 75 mounted to the rotational output shaft 74,with a radial gap provided between the motor stator 73 and the motorrotor 75. The rotational output shaft 74 is cantilevered via twobearings 76 to a cylindrical segment of the inboard housing 83 a of thereducer unit 7.

FIG. 6 shows a longitudinal cross sectional view of a motor (taken alongthe line VI-VI in FIG. 5). The motor rotor 75 of the motor unit 6 mayinclude a rotor core body 79 made of soft magnetic material and may alsoinclude a permanent magnet structure 80 incorporated in the rotor corebody 79. The permanent magnet structure 80 may include permanent magnetsincluding pairs of two neighboring opposed permanent magnets arranged incircular fashion in the rotor core body 79, where, in each of the pairs,the distance between two neighboring opposed permanent magnets increasesalong a length of the opposed permanent magnets, as viewed in a crosssection thereof The permanent magnet structure 80 may include aneodymium magnet. The motor stator 73 may include a stator core body 77made of soft magnetic material and may also include coils 78. The statorcore body 77 has a ring-shaped outer peripheral surface having acircular cross section. The stator core body 77 also has an innerperipheral surface having a circumferentially arranged plurality ofteeth 77 a formed therein that are protruding radially inwards. Thecoils 78 are wound around the corresponding teeth 77 a of the statorcore body 77.

The motor unit 6 as shown in FIG. 5 is associated with an angle sensor36 configured to sense a rotational angle of the motor rotor 75 relativeto the motor stator 73. The angle sensor 36 includes an angle sensorbody 70 configured to sense signals representing a rotational angle ofthe motor rotor 75 relative to the motor stator 73 for output and alsoincludes an angle calculation circuit 71 configured to calculate arotational angle based on the signals produced from the angle sensorbody 70. The angle sensor body 70 includes a detectable element 70 aassociated with the outer peripheral surface of the rotational outputshaft 74 and also includes a detector element 70 b associated with themotor housing 72. For example, the detector element 70 b may bepositioned adjacent the detectable element 70 a in a radially opposedfashion. The detectable element 70 a and the detector element 70 b maybe positioned adjacent each other in an axially opposed fashion. Here,the angle sensor 36 may include a resolver. To maximize the efficiencyof the illustrated motor unit 6, a motor drive controller 33 of a motorcontrol circuitry 29 may be configured to control the timings at whichrespective phase alternating currents are supplied to the coils 78 ofthe motor stator 73, based on the rotational angle of the motor rotor 75relative to the motor stator 73 as sensed by the angle sensor 36.

A connector 99 may be formed at the motor housing 72 for connection ofthe wires for a motor current in the in-wheel motor drive system 8,wires for various sensors, wires for various commands, and etc.

The illustrated reducer unit 7 includes a cycloidal reducer asdescribed. As shown in FIG. 7, the cycloidal reducer includes twocurvilinear plates 84 a, 84 b, each having an outer contour defined by asmoothly corrugated trochoidal curve, that are mounted via respectivebearings 85 to the eccentric segments 82 a, 82 b of the rotational inputshaft 82. A plurality of outer pins 86 are fitted to the housing 83 b todirectly or indirectly guide, along the outer peripheries thereof, theeccentric motions of the curvilinear plates 84 a and 84 b. A pluralityof inner pins 88, which are fitted to the inboard member 60 of the innermember 52, are inserted to a plurality of corresponding, round throughholes 89 formed in each of the curvilinear plates 84 a and 84 b, todirectly or indirectly engage with the through holes 89. The rotationalinput shaft 82 is splinedly connected to the rotational output shaft 74of the motor unit 6 for co-rotation. The rotational input shaft 82 issupported on both sides thereof, via two bearings 90, by an inboardhousing 83 a and by an inner diameter surface of the inboard member 60of the inner member 52.

Rotation of the rotational output shaft 74 of the motor unit 6 causesthe curvilinear plates 84 a, 84 b, associated with the rotational inputshaft 82 that co-rotates with the rotational output shaft 74, to makeeccentric motions. The eccentric motions of the curvilinear plates 84 a,84 b are, through the inner pins 88 directly or indirectly engaging withthe through holes 89, transmitted in the form of a rotary motion to theinner member 52. The speed of rotation of the inner member 52 is reducedwith respect to that of rotation of the rotational output shaft 74. Forexample, a single-stage reducer unit having such a configuration canachieve a reduction ratio of 1/10 or greater.

The two curvilinear plates 84 a, 84 b are mounted, 180° out of phasewith each other, to the eccentric segments 82 a and 82 b of therotational input shaft 82, so that the eccentricity of the motions ofthe curvilinear plates 84 a, 84 b can be cancelled. Counterweights 91associated with the respective eccentric segments 82 a, 82 b, are eachdisposed at a side of the corresponding one of the eccentric segments 82a, 82 b, in such a way that the counterweights 91 face each other acrossthe eccentric segments 82 a, 82 b while each of the counterweights 91being displaced in a direction opposite to the direction of displacementof the corresponding one of the eccentric segments 82 a, 82 b. In thisway, vibrations that may be caused by the curvilinear plates 84 a, 84 bcan be cancelled out.

As shown on an enlarged scale in FIG. 8, bearings 92 and bearings 93 maybe fitted to the outer pins 86 and the inner pins 88, respectively. Theouter rings 92 a of the bearings 92 are in rolling contact with theouter peripheries of the curvilinear plates 84 a, 84 b, while the outerrings 93 a of the bearings 93 are in rolling contact with the innerperipheries of the through holes 89. This can minimize the contactfriction between the outer pins 86 and the outer peripheries of thecurvilinear plates 84 a, 84 b and the contact friction between the innerpins 88 and the inner peripheries of the through holes 89, thus allowingfor smoother transmission of the eccentric motions of the curvilinearplates 84 a, 84 b in the form of a rotary motion to the inner member 52.

The wheel bearing unit 4 of the in-wheel motor drive system 8 as shownin FIG. 5 is secured to a vehicle body through the connection between asuspension system (not shown) such as a knuckle and the housing 83 b ofthe reducer unit 7 or an outer periphery of the housing 72 of the motorunit 6.

A control system will be briefly discussed. A control system U1 as shownin FIG. 1 includes an ECU 21 which is an electronic control unitconfigured to perform general control of the vehicle and an inverterunit 22 configured to perform control of the traction motor units 6, 6according to commands from the ECU 21. The vehicle body 1 is equippedwith the ECU 21, the inverter unit 22, and a braking controller unit 23.The ECU 21 may include a computer, programs that may be executed by thecomputer, and various electronic circuits.

The ECU 21 may be generally divided, in terms of their functions, into adrive control subunit 21 a and a general control subunit 21 b. The drivecontrol subunit 21 a is configured to generate anaccelerating/decelerating command, which will influence the tractionmotor units 6, 6 of the left and right wheels, based on an acceleratingsignal produced from an accelerator manipulation unit 16, a deceleratingsignal produced from a brake manipulation unit 17, and a corneringsignal produced from the steering angle sensor 15, and to send theaccelerating/decelerating command to the inverter unit 22. In addition,the drive control subunit 21 a may be configured to correct theaccelerating/decelerating command, based on information indicating therotational frequency of tire(s) produced from rotation sensor(s) 24 thatis/are operatively associated with the wheel bearing units 4, 5 for therespective wheels 2, 3 and/or information produced from various sensorsthat may be mounted to the vehicle. The accelerator manipulation unit 16includes an accelerator pedal and a sensor 16 a configured to sense thedepression of the accelerator pedal to generate the aforementionedaccelerating signal. The brake manipulator unit 17 includes a brakepedal and a sensor 17 a configured to sense the depression of the brakepedal to generate the aforementioned decelerating signal.

The general control subunit 21 b of the ECU 21 is configured to send thedecelerating command produced from the brake manipulator unit 17 to thebraking controller unit 23, control various auxiliary systems 25,process input signals from an operation panel 26 on a console, cause adisplay 27 to show information, and/or etc. Examples of the auxiliarysystems 25 include an air conditioner, a lamp, a wiper, a GPS, and anairbag. In FIG. 1, the auxiliary systems 25 are indicated in general bya single block.

The braking controller unit 23 is configured to send a braking commandto the brakes 9, 10 equipped to the wheels 2, 3, according to thedecelerating command received from the ECU 21. Commands related tobraking produced from the ECU 21 may include, other than commandsgenerated based on the decelerating signal produced from the brakemanipulator unit 17, a command generated by a safety enhancement subunitthat may be included in the ECU 21. The braking controller unit 23 mayalso include an anti-lock-braking system. The braking controller unit 23may include electronic circuits and/or a microcomputer.

The inverter unit 22 includes a power circuitry 28, which may beprovided one for each of the motor units 6, and a motor controlcircuitry 29 configured to control the power circuitry/circuitries 28. Acommon motor control circuitry 29 may be provided for different powercircuitries 28. Independent motor control circuitries 29 may be providedfor respective different power circuitries 28. Such a common motorcontrol circuitry 29 will be configured to control the different powercircuitries 28 independently of each other, for example, to achievedifferent motor torques. The motor control circuitry 29 may beconfigured to send various information related to the in-wheel motor 8(which may be referred to as “IWM system information”) held by the motorcontrol circuitry 29, such as a variety of detected values or variouscontrol values, to the ECU.

FIG. 2 is a block diagram of a schematic configuration of severalfeatures including the inverter unit 22. The illustrated power circuitry28 include an inverter 31 configured to convert a DC power from abattery unit 19 into a three-phase AC power used to drive the motor unit6 and also include a PWM driver 32 configured to control the inverter31. The motor unit 6 may include a three-phase synchronous motor. Theinverter 31 may include a plurality of semiconductor switching devices(not shown). The PWM driver 32 may be configured to perform pulse widthmodulation on a received current command by generating ON/OFF commandsto the semiconductor switching devices.

The motor control circuitry 29 may include a computer, programs that maybe executed by the computer, and various electronic circuits. The motorcontrol circuitry 29 may include a motor drive controller 33 whichserves as a basic control component. The motor drive controller 33 maybe configured to receive the accelerating/decelerating command such as atorque command from the ECU which serves as an upper-level control unit,convert the accelerating/decelerating command into a current command,and send the current command to the PWM driver 32 of the power circuitry28. The motor drive controller 33 may be configured to obtain a motorcurrent that flows from the inverter 31 to the motor unit 6, with acurrent sensor 35, and perform a current feedback control. The motordrive controller 33 may be configured to obtain a rotational angle ofthe motor unit 6, with an angle sensor 36, and perform a vector control.

In the embodiment under discussion, the motor control circuitry 29 mayinclude a motor current reducer 95 and an abnormalities notifier 41, andthe ECU 21 may include an abnormalities display controller 42, asdescribed below. Furthermore, a temperature sensor Sma may be associatedwith the motor coils 78 (FIG. 5) of the motor unit 6, which isconfigured to sense temperature Tmc of the motor coils 78.

The motor current reducer 95 may reduce a motor current of the motorunit 6. The motor current reducer 95 may, if the temperature Tmc of themotor coils 78 sensed by the temperature sensor Sma exceeds a predefinedmotor coils temperature threshold, reduce a motor current of the motorunit 6 until a derivative dTmc/dt of the sensed temperature Tmc withtime t drops to zero or below. In particular, the motor current reducer95 may include a determiner 39 and a controller 40.

The temperature sensor Sma may include a thermistor. Such a thermistormay be fixed in contact with the motor coils 78 to sense the temperatureTmc of the motor coils 78. In the example under discussion, such asshown in FIG. 2 and FIG. 3, a thermistor may produce a sensed value thatis subsequently amplified by an amplifier Ap, and the determiner 39 maymake determination based on the resulting value.

The determiner 39 may continuously determine if the temperature Tmcsensed by the temperature sensor Sma exceeds a predefined motor coilstemperature threshold. Such a threshold can be appropriately selectedbased on a relationship between time and the temperature of the motorcoils 78 at which insulation on the motor coils deteriorates. Such arelationship may be determined in advance through experiments and/orsimulations. Whether insulation on the motor coils 78 has deterioratedmay be determined based on comparison of an actual motor current for agiven motor voltage applied to the motor unit 6 with a normal value ofthe motor current for the given motor voltage where insulation on themotor coils 78 does not deteriorate. A motor voltage may be sensed by avoltage sensor (not shown) that may be disposed downstream of thecurrent sensor 35. A motor current may be sensed by the current sensor35. A motor coils temperature threshold that may be defined in this waymay be stored in a memory (not shown) in a rewritable manner as a table.

The controller 40 may, if it is determined that the sensed temperatureTmc of the motor coils 78 exceeds a predefined motor coils temperaturethreshold, send through the motor drive controller 33 to the powercircuitry 28 a command that reduces a motor current of the motor unit 6.The motor current may be reduced by a predefined proportion (e.g., 90%)or by a predefined value. Subsequently, the controller 40 may, upondetecting the sign that the rate of change of the sensed temperature Tmcis dropping to zero or below or if the rate of increase of thetemperature represented by the aforementioned dTmc/dt drops to zero orbelow, stop carrying out the control that reduces the motor current,without waiting for the sensed temperature Tmc itself to drop down to acertain value. This prevents drastic hindrance of the driving of themotor unit 6. The aforementioned dTmc/dt dropping to zero or below isequivalent to the slope of the temperature Tmc at a given moment beingzero or below. The temperature of the motor coils 78 may not drop soquickly. Hence, waiting for a certain drop of the temperature to beachieved by reducing a motor current would result in drastic hindranceof the driving of the motor unit 6, thus hindering the driving of thevehicle. In contrast, the aforementioned configuration of stoppingcarrying out control that reduces a motor current upon detecting thesign that the temperature has started to drop can prevent variousproblems that may be caused by drastic hindrance of the driving of amotor unit 6.

Where the sensed temperature Tmc of the motor coils 78 begins toincrease after the motor current reducer 95 stops carrying out theaforementioned control, the motor current reducer 95 may, if the sensedtemperature Tmc is equal or greater than the motor coils temperaturethreshold, resume carrying out the control that reduces the motorcurrent of the motor unit 6. This ensures that overload is avoided, in aconfiguration where the motor current reducer 95 may, if theaforementioned rate of increase of the temperature drops to zero orbelow, stop carrying out the control that reduces the motor current. Inparticular, refer to characteristic diagrams of FIG. 4A and FIG. 4B,each showing a relationship between time t and the temperature Tmc ofmotor coils 78 of a motor unit 6 for the illustrated electric vehicle.

Referring to FIG. 4A, the temperature Tmc of the motor coils 78 maybegin to increase, and at time t1, the determiner 39 may determine thatthe temperature Tmc of the motor coils 78 exceeds a motor coilstemperature threshold Ema. The controller 40 may, in response to such adetermination result, send through the motor drive controller 33 to thepower circuitry 28 a command that reduces a motor current of the motorunit 6. In particular, the motor drive controller 33 may, in response tosuch a command received from the controller 40, send to the PWM driver32 of the power circuitry 28 a current command that causes a currentsupplied to the motor unit 6 to be reduced.

At time t2 where the rate of increase of the temperature represented bythe aforementioned dTmc/dt drops to zero (i.e., the sensed temperatureTmc becomes static), the controller 40 may stop carrying out controlthat reduces a motor current of the motor unit 6. In the example asshown in FIG. 4A, after the time t2, the aforementioned dTmc/dt staysnegative (i.e., the sensed temperature Tmc continues to drop). Thus, thecontroller 40 may, even though the sensed temperature Tmc still exceedsor equals the motor coils temperature threshold Ema, stop carrying outcontrol that reduces a motor current, without waiting for the sensedtemperature Tmc itself to drop to the motor coils temperature thresholdEma or below.

Referring to FIG. 4B, at time t1, the controller 40 may, in response toa determination result produced from the determiner 39, send through themotor drive controller 33 to the power circuitry 28 a command thatreduces a motor current of the motor unit 6. After time t2 where themotor current reducer 95 stops carrying out control that reduces a motorcurrent, the sensed temperature Tmc of the motor coils 78 may begin toincrease. At time t3, the controller 40 may, in response to thedetermination that the sensed temperature Tmc equals or exceeds themotor coils temperature threshold, resume carrying out control thatreduces a motor current of the motor unit 6. Subsequently, thecontroller 40 may, if the rate of increase of the temperature drops tozero or below, stop carrying out control that reduces a motor current.This ensures that overload is avoided.

The abnormalities notifier 41 as shown in FIG. 2 may be configured tosend information indicating abnormalities to the ECU 21, if thedeterminer 39 determines that the sensed temperature Tmc exceeds themotor coils temperature threshold.

The abnormalities display controller 42, which may be included in theECU 21, may be configured to, in response to the information indicatingabnormalities of the motor unit 6 produced from the abnormalitiesnotifier 41, cause a vehicle driver display 27 to show a presentationthat indicates abnormalities. The presentation that can be shown on thedisplay 27 may include a presentation with letters and/or symbols, suchas an icon.

The following advantages or effects may be achieved. In theaforementioned configuration, the temperature sensor Sma maycontinuously sense the temperature Tmc of the motor coils 78. Theelectric vehicle may be driven for a continuous time with a highertorque in order to, for example, go up a slope. This can lead toincrease in the temperature Tmc of the motor coils 78. The determiner 39may determine if the sensed temperature Tmc exceeds a predefined motorcoils temperature threshold. The controller 40 may, if it is determinedthat the sensed temperature Tmc exceeds the motor coils temperaturethreshold, send to the power circuitry 28 a command that reduces a motorcurrent of the motor unit 6. Subsequently, the controller 40 may, upondetecting the sign that the rate of change of the sensed temperature Tmcis dropping to zero or below or if the rate of increase of thetemperature represented by the aforementioned dTmc/dt drops to zero orbelow, stop carrying out the control that reduces the motor current,without waiting for the sensed temperature Tmc itself to drop down to acertain value. This prevents drastic hindrance of the driving of themotor unit 6.

If the sensed temperature Tmc of the motor coils 78 begins to increaseonce the motor current reducer 95 stops carrying out the aforementionedcontrol, the motor current reducer 95 may, once the sensed temperatureTmc equals or exceeds the motor coils temperature threshold, resumecarrying out the control that reduces the motor current of the motorunit 6. Subsequently, the motor current reducer 95 may, if theaforementioned rate of increase of the temperature drops to zero orbelow, stop carrying out the control that reduces the motor current.This ensures that overload is avoided.

In the aforementioned configuration, the motor control circuitry 29 ofthe inverter unit 22 includes the motor current reducer 95. In this way,the motor current reducer 95 that may make the aforementioneddetermination based on the sensed temperature is positioned closer tothe motor unit 6 than in a configuration where the ECU 21 includes themotor current reducer 95, thus the former configuration being moreadvantageous in terms of wire routing. Also, with the formerconfiguration, an appropriate control can be initiated more quickly thanwith a configuration of the ECU 21 including the motor current reducer95, thus promptly avoiding various driving problems. Furthermore, withthe former configuration, the load on the ECU 21, whose complexity isincreasing hand-in-hand with its sophistication, can be reduced.

The ECU 21 performs general, integrated control of the vehicle. Thus, bysending to the ECU 21 a notification of abnormalities of the motor unit6 if it is found, with the motor current reducer 95 that may be includedin the inverter unit 22, that there is abnormalities of the motor coils78, the ECU 21 can correspondingly perform an appropriate control of thevehicle in general. Also, the ECU 21 is an upper-level control unitwhich may send a drive command to the inverter unit 22. Thus, an urgentcontrol performed by the inverter unit 22 may be followed by a moreappropriate control of drive which is performed by the ECU 21.

Reliability of the wheel bearing unit 4, the reducer unit 7 and themotor unit 6 is an urgent concern for an in-wheel motor drive system 8which, due to its smaller size, has less materials used, involves rapidrotation of the motor unit 6, and etc. Sensing the temperature of themotor coils 78 and continuously monitoring the motor coils 78 forabnormalities such as deterioration of insulation enables responsivecontrol that appropriately reduces the motor current of the motor unit6.

In the aforementioned configuration, the reducer unit 7 in the in-wheelmotor drive system 8 includes a cycloidal reducer having, for example, areduction ration of 1/6 or greater. This allows for the provision of asmaller motor unit 6, thus achieving reduction in dimensions of thesystem or assembly. With such a significant reduction ratio, a smallermotor unit 6 may involve rapid rotation. Even when a motor unit 6 isundergoing rapid rotation, early detection of abnormalities such asdeterioration of insulation on the motor coils 78 of the motor unit 6can be realized, thus enabling appropriate measures to be promptlytaken.

The motor current of the motor unit 6 may be reduced by a predefinedproportion. For example, the motor current of the motor unit 6 may bereduced, after every certain period of time, by a certain percentagerelative to the original motor current. For another example, theproportion by which the motor current of the motor unit may be reducedmay, after every certain period of time, be incremented. As shown inFIG. 9 which illustrates an electric vehicle according to the secondembodiment, the ECU 21 which is an electronic control unit configured toperform general control of the vehicle may include the motor currentreducer 95.

An electric vehicle according to the third embodiment and the fourthembodiment of the present invention will be discussed below. Note thatthose features corresponding to the features already described withreference to the preceding embodiment(s) will be given the samereference signs and will not be described. In the discussion of a givenconfiguration where only certain features are described, the remainingnon-described features should be considered as the same as those alreadydescribed with reference to the preceding embodiment(s). Also note thatbeside the combinations of the features described in detail withreference to a certain embodiment, various embodiments themselves can bepartially combined with each other unless such combinations areinoperable.

Referring to the block diagram of FIG. 10, a schematic configuration ofseveral features including an inverter unit, of an electric vehicleaccording to the third embodiment of the present invention will now bedescribed. In the embodiment under discussion, the motor controlcircuitry 29 may include an inverter limiter 102, which will bedescribed below, as well as an abnormalities notifier 41, and the ECU 21may include an abnormalities display controller 42. Furthermore, atemperature sensor Sia may be associated with the inverter 31, which isconfigured to sense temperature Tic of the inverter 31. The inverterlimiter 102 may limit a current command to the inverter 31. The inverterlimiter 102 may, upon determining that the temperature Tic of theinverter 31 sensed by the temperature sensor Sia exceeds a predefinedinverter temperature threshold, limit a current command to the inverter31 until a derivative dTic/dt of the sensed temperature Tic with time tdrops to zero or below. In particular, the inverter limiter 102 mayinclude a determiner 39A and a controller 40A.

The temperature sensor Sia may include a thermistor. Such a thermistormay be fixed in contact with a substrate to which a plurality ofsemiconductor switching devices may be mounted, to sense the temperatureTic of the inverter 31. A thermistor may be fixed to the semiconductorswitching devices. In the example under discussion, such as shown inFIG. 10 and FIG. 11, a thermistor may produce a sensed value that issubsequently amplified by an amplifier Ap, and the determiner 39A maymake determination based on the resulting value.

The determiner 39A may continuously determine if the temperature Ticsensed by the temperature sensor Sia exceeds a predefined invertertemperature threshold. Such a threshold may be the nominal operatingtemperature of semiconductor switching devices used. The threshold canbe appropriately selected based on a relationship between time and thetemperature of the inverter 31 at which undesirable change in thecharacteristics of the inverter 31 occurs. Such a relationship may bedetermined in advance through experiments and/or simulations. Aninverter temperature threshold that may be defined in this way may bestored in a memory (not shown) in a rewritable manner as a table.

The controller 40A may, if it is determined that the sensed temperatureTic of the inverter 31 exceeds a predefined inverter temperaturethreshold, send through the motor drive controller 33 to the powercircuitry 28 a command that limits a current command to the inverter 31.In particular, the motor drive controller 33 may receive anaccelerating/decelerating command from the ECU 21, convert theaccelerating/decelerating command into a current command, and send thecurrent command to the PWM driver 32. The motor drive controller 33 may,in response to the aforementioned command received from the controller40A, limit such a current command.

More specifically, the controller 40A may carry out control that causeschange in at least one of duty cycle and pulse number. For example, thecontrol that limits a current command to the inverter 31 may includereduction of a duty cycle, which indicates pulse ON time per switchingperiod, below a predefined duty cycle by several tens of percentrelative to the predefined duty cycle, thus reducing effective voltagevalue, or may include generation of pulses of unequal width whilemaintaining a switching period.

Subsequently, the controller 40A may, upon detecting the sign that therate of change of the sensed temperature Tic is dropping to zero orbelow or if the rate of increase of the temperature represented by theaforementioned dTic/dt drops to zero or below, stop carrying out thecontrol that limits a current command to the inverter 31, withoutwaiting for the sensed temperature Tic itself to drop down to a certainvalue. This can avoid excessive reduction of a motor current, thuspreventing drastic hindrance of the driving of the motor unit 6. Theaforementioned dTic/dt dropping to zero or below is equivalent to theslope of the temperature Tic at a given moment being zero or below.

The temperature of the inverter 31 may not drop so quickly. Hence,waiting for a certain drop of the temperature to be achieved by limitinga current command to the inverter 31—thus by reducing a motorcurrent—would result in drastic hindrance of the driving of the motorunit 6, thus hindering the driving of the vehicle. In contrast, theaforementioned configuration of stopping carrying out control thatlimits a current command to the inverter 31—thus stopping carrying outcontrol that reduces a motor current of the motor unit—upon detectingthe sign that the temperature has started to drop can prevent variousproblems that may be caused by drastic hindrance of the driving of amotor unit 6.

If the sensed temperature Tic of the inverter 31 begins to increaseafter the inverter limiter 102 stops carrying out the aforementionedcontrol, the inverter limiter 102 may, once the sensed temperature Ticequals or exceeds the inverter temperature threshold, resume carryingout the control that limits a current command to the inverter 31.Subsequently, the inverter limiter 102 may, if the aforementioned rateof increase of the temperature drops to zero or below, stop carrying outthe control that limits a current command to the inverter 31. Thisensures that overload is avoided. In this way, the change ofcharacteristics of the inverter 31 and/or a damage to the inverter 31that may be caused by overheat can be prevented, thus preventingundesirable change in the control characteristics of the driving of themotor unit and/or preventing a situation where the driving of the motorunit is impossible. In particular, refer to characteristic diagrams ofFIG. 12A and FIG. 12B, each showing a relationship between time t andthe temperature Tic of an inverter 31 for the illustrated electricvehicle.

Referring to FIG. 12A, the temperature Tic of the inverter 31 may beginto increase, and at time t1, the determiner 39A may determine that thetemperature Tic of the inverter 31 exceeds an inverter temperaturethreshold Eia. The controller 40A may, in response to such adetermination result, send through the motor drive controller 33 to thepower circuitry 28 a command that limits a current command to theinverter 31. In particular, the motor drive controller 33 may, inresponse to such a command received from the controller 40A, send to thePWM driver 32 of the power circuitry 28 a current command that causes acurrent supplied to the motor unit 6 to be reduced.

At time t2 where the rate of increase of the temperature represented bythe aforementioned dTic/dt drops to zero (i.e., the sensed temperatureTic becomes static), the controller 40A may stop carrying out controlthat limits a current command to the inverter 31. In the example asshown in FIG. 12A, after the time t2, the aforementioned dTic/dt staysnegative (i.e., the sensed temperature Tic continues to drop). Thus, thecontroller 40A may, even though the sensed temperature Tic still exceedsor equals the inverter temperature threshold Eia, stop carrying outcontrol that limits a current command, without waiting for the sensedtemperature Tic itself to drop to the inverter temperature threshold Eiaor below.

Referring to FIG. 12B, at time t1, the controller 40A may, in responseto a determination result produced from the determiner 39A, send throughthe motor drive controller 33 to the power circuitry 28 a command thatlimits a current command to the inverter 31. After time t2 where theinverter limiter 102 stops carrying out control that limits a currentcommand, the sensed temperature Tic of the inverter 31 may begin toincrease. At time t3, the controller 40A may, in response to thedetermination that the sensed temperature Tic equals or exceeds theinverter temperature threshold, resume carrying out control that limitsa current command to the inverter 31. Subsequently, the controller 40Amay, if the rate of increase of the temperature drops to zero or below,stop carrying out control that limits a current command to the inverter31. This ensures that overload is avoided.

The following advantages or effects may be achieved. In theaforementioned configuration, the temperature sensor Sia maycontinuously sense the temperature Tic of the inverter 31. The electricvehicle may be driven for a continuous time with a higher torque inorder to, for example, go up a slope. This can lead to increase in thetemperature Tic of the inverter 31 as well as increase in thetemperature Tmc of the motor coils 78. The determiner 39A may determineif the sensed temperature Tic exceeds a predefined inverter temperaturethreshold. The controller 40A may, if it is determined that the sensedtemperature Tic exceeds the inverter temperature threshold, send to thepower circuitry 28 a command that limits a current command to theinverter 31. Subsequently, the controller 40A may, upon detecting thesign that the rate of change of the sensed temperature Tic is droppingto zero or below or if the rate of increase of the temperaturerepresented by the aforementioned dTic/dt drops to zero or below, stopcarrying out the control that limits a current command to the inverter31, without waiting for the sensed temperature Tic itself to drop downto a certain value. This can avoid excessive reduction of a motorcurrent, thus preventing drastic hindrance of the driving of the motorunit 6.

If the sensed temperature Tic of the inverter 31 begins to increaseafter the inverter limiter 102 stops carrying out the aforementionedcontrol, the inverter limiter 102 may, once the sensed temperature Ticequals or exceeds the inverter temperature threshold, resume carryingout the control that limits a current command to the inverter 31.Subsequently, the inverter limiter 102 may, if the aforementioned rateof increase of the temperature drops to zero or below, stop carrying outthe control that limits a current command to the inverter 31. Thisensures that overload is avoided. In this way, the change ofcharacteristics of the inverter 31 and/or a damage to the inverter 31that may be caused by overheat can be prevented, thus preventingundesirable change in the control characteristics of the driving of themotor unit and/or preventing a situation where the driving of the motorunit is impossible.

In the aforementioned configuration, the motor control circuitry 29 ofthe inverter unit 22 includes the inverter limiter 102. In this way, theinverter limiter 102 that may make the aforementioned determinationbased on the sensed temperature is positioned closer to the motor unit 6than in a configuration where the ECU 21 includes the inverter limiter102, thus the former configuration being more advantageous in terms ofwire routing. Also, with the former configuration, an appropriatecontrol can be initiated more quickly than with a configuration of theECU 21 including the inverter limiter 102, thus promptly avoidingvarious driving problems. Furthermore, with the former configuration,the load on the ECU 21, whose complexity is increasing hand-in-hand withits sophistication, can be reduced.

The ECU 21 performs general, integrated control of the vehicle. Thus, bysending to the ECU 21 a notification of abnormalities of the inverter 31if it is found, with the inverter limiter 102 that may be included inthe inverter unit 22, that there is temperature abnormalities of theinverter 31, the ECU 21 can correspondingly perform an appropriatecontrol of the vehicle in general. Also, the ECU 21 is an upper-levelcontrol unit which may send a drive command to the inverter unit 22.Thus, an urgent control performed by the inverter unit 22 may befollowed by a more appropriate control of drive which is performed bythe ECU 21.

Sensing the temperature of the inverter 31 and continuously monitoringthe inverter 31 for abnormalities, such as thermal runaway caused byoverheat of semiconductor switching devices enables responsive controlthat appropriately limits a current command to the inverter 31.

Even when a motor unit 6 is undergoing rapid rotation, the change ofcharacteristics of an inverter 31 and/or a damage to the inverter can beprevented, thus preventing undesirable change in the controlcharacteristics of the driving of the motor unit and/or preventing asituation where the driving of the motor unit is impossible. Thisenables avoiding a situation where driving of a vehicle is suddenlyimpossible.

As shown in FIG. 13 which is similar to FIG. 9 but illustrates anelectric vehicle according to the fourth embodiment, the ECU 21 which isan electronic control unit configured to perform general control of thevehicle may include the inverter limiter 102.

Although the present invention has been described in connection withpreferred embodiments with reference to the accompanying drawings whichare used only for the purpose of illustration, those skilled in the artwill readily conceive numerous changes and modifications within theframework of obviousness upon the reading of the specification hereinpresented of the present invention. Accordingly, such changes andmodifications are, unless they depart from the scope of the presentinvention as delivered from the claims annexed hereto, to be construedas included therein.

REFERENCE SIGNS

2: Wheel

4: Wheel bearing unit

6: Motor unit

7: Reducer unit

8: In-wheel motor drive system

19: Battery unit

21: ECU

22: Inverter unit

28: Power circuitry

29: Motor control circuitry

31: Inverter

39: Determiner in motor current reducer

39A: Determiner in inverter limiter

40: Controller in motor current reducer

40A: Controller in inverter limiter

41: Abnormalities notifier

78: Motor coil

95: Motor current reducer

102: Inverter limiter

Sma: Motor temperature sensor

Sia: Inverter temperature sensor

U1: Control system

1. An electric vehicle comprising: a motor unit configured to drive awheel, the motor unit including motor coils; a control system thatcontrols the motor unit, the control system including an inverter; atemperature sensor that is associated with the motor coils of the motorunit and is configured to sense temperature Tmc of the motor coils or atemperature sensor that is associated with the inverter and isconfigured to sense temperature Tic of the inverter; and a limiterconfigured to, if the temperature Tmc sensed by the temperature sensoris equal to or greater than a motor coils temperature threshold, reducea motor current of the motor unit until a derivative dTmc/dt of thesensed temperature Tmc with time t drops to zero or below, or to, if thetemperature Tic sensed by the temperature sensor is equal to or greaterthan an inverter temperature threshold, limit a current command to theinverter until a derivative dTic/dt of the sensed temperature Tic withtime t drops to zero or below, the limiter being further configured to,when the dTmc/dt or dTic/dt drops to zero or below, stop reducing amotor current of the motor or limiting the current command to theinverter.
 2. The electric vehicle as claimed in claim 1, wherein thecontrol system includes an ECU which is an electronic control unitconfigured to perform general control of the vehicle and also includesan inverter unit, the inverter unit including a power circuitry whichincludes the inverter and also including a motor control circuitryconfigured to control at least the power circuitry in accordance withcontrol from the ECU; and wherein the inverter is configured to converta DC power from a battery unit into an AC power used to drive the motorunit.
 3. The electric vehicle as claimed in claim 2, wherein the motorcontrol circuitry includes the limiter; and wherein the limiter includesa determiner configured to determine if the temperature sensed by thetemperature sensor exceeds the motor coils temperature threshold or theinverter temperature threshold and also includes a controller configuredto send to the power circuitry, if it is determined that the sensedtemperature exceeds the motor coils temperature threshold or theinverter temperature threshold, a command that reduces the motor currentof the motor unit or a command that limits the current command to theinverter.
 4. The electric vehicle as claimed in claim 3, wherein theinverter unit includes an abnormalities notifier configured to send tothe ECU a notification of abnormalities of the motor unit if thedeterminer determines that the sensed temperature exceeds the motorcoils temperature threshold or a notification of abnormalities of theinverter if the determiner determines that the sensed temperatureexceeds the inverter temperature threshold.
 5. The electric vehicle asclaimed in claim 1, further comprising: a wheel bearing unit; and areducer unit; wherein the motor unit, together with the wheel bearingunit and the reducer unit, forms an in-wheel motor drive system that ispartly or entirely disposed within the wheel.
 6. The electric vehicle asclaimed in claim 1, further comprising: a reducer unit configured toproduce rotation with a speed that is reduced with respect to that ofrotation of the motor unit, wherein the reducer unit comprises acycloidal reducer.